Modern common rail fuel systems typically include multiple fuel injectors connected to a common rail that is supplied with high-pressure fuel by a high-pressure fuel pump. To enable the utilization of different injection strategies (e.g., different injection timings, volumes, etc.), the high-pressure fuel pump is usually a variable discharge pump. One type of variable discharge pump is an outlet metered, camshaft driven pump. In many cases, these pumps include a driven gear coupled to the camshaft of the pump that is driven by a driving gear provided within the geartrain on the front of the engine, which ultimately receives its power from a gear coupled to the engine crankshaft.
A camshaft driven, outlet metered pump generally includes multiple plunger assemblies, each including a plunger that is disposed within an individual pumping chamber or bore. Each of the plunger assemblies is configured to engage a lobe of the camshaft such that the rotation of the camshaft causes the plunger to reciprocate within its bore between a top dead center position and a bottom dead center position. The plunger acts to pressurize and eventually displace fuel (to the common rail) from the pumping chamber when it moves from its bottom dead center position to its top dead center (its pumping stroke), and allows the pumping chamber to refill with fuel when it moves from its top dead center position to its bottom dead center position (its refilling stroke). The amount of fuel pumped by each plunger to the common rail will depend on the amount of fluid spilled or diverted to a low-pressure reservoir during the pumping stroke of the plunger. Due to the nature of the pump, the torque resistance it applies to the geartrain system will fluctuate. The torque resistance fluctuation is due, at least in part, to the different stages the plungers pass through during a revolution of the pump camshaft as well as to the varying output demands placed on the pump over time.
Although such a pump serves to effectively pressurize fuel for a common rail fuel system, its cyclical and varying operation, as well as the torque resistances it provides may have an effect on the geartrain that powers the pump. One source of this effect is due primarily to the nature of gears. When two gears mesh, the imperfections of the individual gear teeth (albeit very small in many cases) create a situation where some cooperating teeth may align properly while others may be slightly misaligned. Thus, as one set of teeth goes out of engagement, there may be a small gap between the next cooperating set of teeth. One of the two cooperating gears may then accelerate until the gears impact one another. The magnitude of the loads generated from these impacts will depend on the magnitude of the torques being transferred between the gears. In general, as the torques transferred between the gears become higher, the impact loads become higher. At some point, the impact loads can potentially result in gear damage. In addition, the impacts between the gear teeth can also produce undesirable noise. The cyclical and varying operation of the pump may also contribute to higher impact loads and noise. For example, in some cases, the pump may be configured such that at certain points within its operating cycle the pump actually produces negative torque resistance to the system, which may temporarily create gear teeth separation, which will then result in gear teeth impacts when the torque resistance of the pump shortly thereafter becomes positive again. Moreover, inertial forces, as well as the resilient nature of some components when exposed to high torques, may also create situations where gear teeth momentarily separate and then impact one another when the teeth come back together, resulting in high impact loads and noise.
A torsional vibration damper is described in U.S. Pat. No. 6,402,621, which includes an input element and an output element, both rotatable against the action of a damping means. The damping means includes a plurality of linkages, each linkage comprising a plurality of interconnected links configured to act upon a plurality of spring members. At least one of the interconnected links is flexible in an axial direction relative to the remainder of the damping means to accommodate relative tilting of the damper elements. Although the described damper may provide sufficient damping in certain applications, it should be appreciated that there is a continuing need for improved damping means in various applications. Further, there is a need for damping assemblies having improved performance that may be used in applications subject to strict spatial constraints.
The present disclosure is directed to one or more of the problems set forth above.